There have heretofore been known display apparatus including cathode-ray tubes (CRT), liquid crystal display panels, plasma display panels, etc.
Cathode-ray tubes include ordinary television receivers and monitors for use with computers. While the cathode-ray tubes can produce bright rasters, they consume large electric energy and have a depth that increases in proportion to the raster size. The cathode-ray tubes are also disadvantageous in that the resolution is lowered at peripheral edges of displayed images, resulting in distortions of displayed images or figures, there is no storage capability, and no large-size display is available.
The reasons for these shortcomings are that since the electron beam radiated from the electron gun is largely deflected, the beam spot is spread in areas where the electron beam arrives obliquely at the phosphor surface of the cathode-ray tube, displaying an image obliquely and distorting the displayed image, and that there is a limitation on efforts to keep the large space in a vacuum within the cathode-ray tube.
Liquid crystal display panels can be reduced in overall size and consume small electric energy, but are low in raster luminance and provide a limited angle of view. The liquid crystal display panels also suffer difficulty in that their drive circuit is very complex because image gradations are expressed by way of voltage levels.
For example, in the case where digital data lines are employed, the drive circuit therefor comprises a latch circuit for holding component RGB data (each of 8 bits) for a given period of time, a voltage selector, a multiplexer for switching between as many voltage levels as the number of gradations, and an output circuit for applying output data from the multiplexer to the digital data lines. As the number of gradations increases, the multiplexer needs to switch between many voltage levels and hence requires a complex circuit arrangement.
In the case where analog data lines are employed, the drive circuit therefor comprises a shift register for arraying successively inputted component RGB data (each of 8 bits) in a horizontal direction, a latch circuit for holding parallel data from the shift register for a given period of time, a level shifter for regulating a voltage level, a D/A converter for converting output data from the level shifter to an analog signal, and an output circuit for applying an output signal from the D/A converter to the analog data lines. The D/A converter comprises an operational amplifier to produce voltages depending on gradations. If the range of gradations increases, then the D/A converter needs to employ an operational amplifier capable of outputting highly accurate voltages, and hence is complex in arrangement and highly costly.
As with the liquid crystal display panels, plasma display panels can be reduced in size because the display unit itself does not take up a volume, and can easily be viewed because the display surface is flat. Particularly, AC plasma display panels are advantageous in that they require no refresh memory on account of the storage capability of cells.
In order to give a storage capability to the cells of the plasma display panels, it is necessary to alternately switch the polarity of the applied voltage to sustain an electric discharge. To meet this requirement, the drive circuit needs to have a first pulse generator for generating sustaining pulses in an X-direction and a second pulse generator for generating sustaining pulses in a Y-direction. Accordingly, the drive circuit is necessarily complex in arrangement.
The applicant of the present application has proposed a novel display apparatus in efforts to solve the problems of the CRTs, the liquid crystal display panels, and the plasma display panels (see, for example, Japanese laid-open patent publication No. 7-287176). As shown in FIG. 39 of the accompanying drawings, the proposed display apparatus has actuators 200 arrayed in association with respective pixels. Each of the actuators 200 has an actuator unit 208 comprising a piezoelectric/electrostrictive layer 202 and upper and lower electrodes 204, 206 disposed respectively on upper and lower surfaces of the piezoelectric/electrostrictive layer 202, and a base 214 comprising a vibrator 210 disposed underneath the actuator unit 208 and a mount member 212. The lower electrode 206 of the actuator unit 208 is held in contact with the vibrator 210, which supports the actuator unit 208.
The base 214, which comprises an integral combination of the vibrator 210 and the mount member 212, is made of ceramics. The base 214 has a cavity 216 where the vibrator 210 is of a reduced thickness.
To the upper electrode 204 of the actuator unit 208, there is connected a displacement transfer member 220 for allowing the actuator 200 to contact a light guide plate 218 through an area of a predetermined size. In the example shown in FIG. 39, the displacement transfer member 220 is disposed closely to the light guide plate 218 when the actuator 200 is stationary, and contacts the light guide plate 218 at a distance which is equal to or shorter than the wavelength of light when the actuator 200 is energized.
Light 222 is introduced into the light guide plate 218 from an end thereof, for example. With the refractive index of the light guide plate 218 being adjusted, the light 222 is totally reflected in its entirety without passing through front and rear surfaces of the light guide plate 218. Then, a voltage signal depending on an attribute of an image signal is applied to the actuators 200 through the upper and lower electrodes 204, 206 to keep the actuators 200 stationary in a normal state and displace the actuators 200 in an energized state for thereby controlling the actuators 200 to move into and out of contact with the light guide plate 218. Diffused light (leakage light) 224 in given areas of the light guide plate 218 is thus controlled to display an image depending on the image signal on the light guide plate 218.
The display apparatus offers advantageous in that (1) the electric energy consumption can be reduced, (2) the raster luminance can be increased, and (3) the number of pixels for displaying color images does not need to be increased as compared with the number of pixels for displaying black-and-white images.
A peripheral circuit for the above display apparatus comprises, as shown in FIG. 40 of the accompanying drawings, a display area 230 composed of a matrix of pixels, a vertical shifting circuit 234 from which extend as many vertical selection lines 232 as the number of rows, each vertical selection line 232 being common to a number of pixels (a group of pixels) of one row, and a horizontal shifting circuit 238 from which extend as many horizontal selection lines 236 as the number of columns, each horizontal selection line 236 being common to a number of pixels (a group of pixels) of one column.
Display information (output voltage) outputted from the horizontal shifting circuit 238 to the group of pixels of a selected row is also applied to the groups of pixels of unselected rows, thus necessarily energizing unnecessary pixels (actuators). Therefore, unwanted electric energy is consumed, posing disadvantages in relation to efforts to design the display apparatus for lower electric energy consumption.
In order to select all rows in a vertical scanning period, the pixels can emit light only in a period of time represented by (the vertical scanning period/the number of necessary selected rows), resulting in a limitation on efforts to make the display apparatus more luminous.
One attempt to eliminate the above drawbacks is to provide switching elements in the form of an IC. However, such a scheme needs a number of wires between a drive circuit having as many switching elements as the number of pixels and a board (actuator board) on which the actuators are mounted. It is difficult to form a wiring pattern on the actuator board.
Another solution is to provide horizontal shifting circuits 238 associated with respective rows, as shown in FIG. 41 of the accompanying drawings. However, such an arrangement results in a very complex circuit arrangement.
The present invention has been made in view of the above problems. It is an object of the present invention to provide a display apparatus of the proposed kind which has low electric energy consumption and higher raster luminance, and allows wires or interconnections to be formed with ease.